The Spanish Plume

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  • The Spanish Plume
    19.07.2010 16:23

     

    Three fine days and a thunderstorm. A phrase often heard during the British summer and a phenomenon that often brings an episode of warm summer sunshine abruptly to an end.

    But why are we so often rudely interrupted by such sudden cloudbursts, which always seemingly arrive just as we dust off the barbeque, pop a knotted hanky on to our heads and drag out the deck chairs?
     
    More-often-than-not, it’s all thanks to our foreign neighbours. A typical UK summer usually consists of high pressure ridging in from the Atlantic, which settles down across us to bring those long sunny days and increasing temperatures that most of us seem to long for. 

    However, this high pressure, often referred to as the Azores High, gradually comes under attack by Atlantic depressions trying to continue along their usual path from west to east.

    As these lows begin to encroach in to British territory, so the Azores high eases its way east, introducing a southerly flow that brings with it a blast of hot and humid air from off the continent and its surrounding sea.

    This high humidity is often lying close to the ground whilst higher up in the atmosphere, the air is much drier, with its origins coming from the Spanish interior. This type of set-up brings about a very unstable weather pattern across north-western parts of France and southern areas of Britain.

    All is needed now is a trigger mechanism to spark off those thundery outbreaks we are accustomed to. The excessively high temperatures across France can sometimes be enough to trigger off storms but it usually comes back to those Atlantic low pressure systems queuing up just west of the UK. As the Atlantic depression forces a cold front eastwards, the air aloft is cooled.

    This allows the hot, humid air at the surface to break free high in to the atmosphere and often results in some dramatic thundery downpours. As the southerly flow continues, so the storms drift north across the UK before finally being shoved away to the east as the Atlantic depression drifts in to bring a cooler and sometimes more unsettled spell of weather to the British Isles.
     
    This weather pattern, referred to as a Spanish Plume, can bring about some particularly nasty storms to parts of the UK. Frequent lightning, flash floods, gusty winds and even some very large hail are often observed, and bring to an abrupt end a spell of fine summer weather, and of course those planned barbeques, trips to the coast, picnics in the park, etc, etc.

    By: Gareth Harvey